1. Field of the Invention
The present invention relates to an optical disc drive, and, more particularly, to an optical pickup unit feeding apparatus for an optical disc drive, for feeding an optical pickup unit in a radial direction of an optical disc.
2. Description of the Related Art
Optical disc drives generally record data on, or reproduce data from, disc-shaped media such as CDs, DVDs, or the like. An optical disc drive includes an optical pickup unit feeding apparatus for feeding an optical pickup unit in a radial direction of the optical disc when data is recorded on, or reproduced from, an optical disc.
The optical pickup unit feeding apparatus is generally actuated by a rotary motor. However, since the optical pickup unit has to move from one side of an optical disc to another side along a straight line, the rotary motion of the motor has to be changed into a linear motion. The change of the rotary motion into a linear motion may be performed using a rack gear and a pinion gear or a lead screw.
FIG. 1 is a schematic plan view of an optical pickup unit feeding apparatus using a lead screw. Referring to FIG. 1, a lead screw 20, on which a spiral groove 21 is formed, is rotated while being attached to a driving motor 50. A guide member 30 is combined with an optical pickup unit 10 and includes a contact part 31, which is combined with the spiral groove 21 of the lead screw 20. A coil spring 40 applies an elastic force to the guide member 30 in a direction along which the contact part 31 is combined with the spiral groove 21.
According to the above-described structure, when the lead screw 20 rotates, the contact part 31 moves along the spiral groove 21, and thus the optical pickup unit 10 slides along a guide shaft 60.
FIG. 2 illustrates the relationship between a spring force and a displacement of the coil spring 40. Referring to FIG. 2, since the spring force increases in proportion to the displacement, a spring constant k1, i.e., the inclination of the spring force, is constant.
When the displacement of the coil spring 40 is X1, the spring force F1 is first applied to the contact part 31. Since a rotating force and power consumption of the driving motor 50, which rotates the lead screw 20, increases with an increase in a spring force F1 applied to the contact part 31, it is preferable that the spring force F1 is small. Next, when the lead screw 20 starts rotating, the contact part 31 starts moving while engaging the spiral groove 21. Here, when a reaction force, generated due to inertia of the optical pickup unit 10 and the friction between the optical pickup unit 10 and the guide shaft 60, gets larger than the spring force F1, the contact part 31 is pushed toward the optical pickup unit 10.
If the optical pickup unit feeding apparatus is used for a long period of time, a contact surface between the guide shaft 60 and the optical pickup unit 10 is worn away, or dust piles up on the guide shaft 60. This increases the friction between the guide shaft 60 and the optical pickup unit 10, which further increases the reaction force of the contact part 31, and when the reaction force exceeds a predetermined value F2, the contact part 31 is separated from the spiral groove 21. Thus, the optical pickup 10 fails to move by a predetermined distance in spite of the rotation of the lead screw 20. This phenomenon is called the mis-feeding phenomenon.
The maximum value of the reaction force, which maintains the engagement between the contact part 31 and the spiral groove 21, becomes F2=F1+k1×d, where d denotes the depth of the spiral groove 21. Accordingly, an increase in the spring force F1 can prevent the mis-feeding phenomenon. However, as discussed above, the power consumption of the driving motor 50 increases with an increase in the spring force F1.
Additionally, noise and vibrations, occurring during the rotation of the driving motor 50, propagate through the lead screw 20 to the contact part 31. Since a damping ability of the coil spring 40 is weak, the coil spring 40 transmits noise and vibration up to the optical pickup unit 10, which has a bad effect on recording/reproduction characteristics of the optical disc drive. Also, noise and vibrations may degrade the quality of the optical disc drive.